1. Field of the Invention
This invention relates to the formation of structures on a nanometer size scale.
2. Description of the Prior Art
In recent years interest has increased in the fabrication of electronic, optical and/or biomolecular devices of nanometer size (nanometer structures). An attractive feature of such molecular size devices is the vast number that may be packed into a small area, i.e., the high density that is possible. Computers which incorporate such devices would have significantly increased memory and speed. The incorporation of biological molecules into such devices is also desirable and would be facilitated by the ability to fabricate structures on a nanometer scale. The fabrication of devices on the nanometer level also is desirable since new physical effects not obtainable for larger size devices become important. An example is the patterning of surfaces for utilization of surface enhanced Raman scattering phenomena.
Current methods of producing such nanometer devices include writing on the surface of a substrate or on a substrate covered with an electron sensitive resist material with a focused electron beam. This serial method of device fabrication is, however, limited by the long times required to produce the vast number of nanometer devices possible in small areas (i.e., over 10,000 devices in a micron square area). Additionally, conventional methods do not presently offer convenient means of incorporating active biological molecules into nanometer size devices.
A particularly advantageous method of producing microdevices and micropatterns consists of lithographic reproduction of an existing pattern from a suitable mask onto the device substrate. Such a preexisting pattern is transferred by placing the mask in proximit..y to the underlying substrate. Then the pattern is etched into or applied to the substrate using a variety of methods including exposure to a beam consisting of reactive ions, electromagnetic radiation or reactive molecules. The mask is normally produced by a serial writing method such as focusing an electron beam on a suitably sensitive material such as a resist material. Current lithographic methods are limited by the size of the individual features which can be embedded in a mask, the size of the mask as well as the time necessary to produce these masks. In particular, currently employed lithographic masks will typically have features which are micron in dimension whereas nanometer microdevice fabrication requires masks containing nanometer scale details. While serial writing of such a pattern on a nanometer scale is possible, using known methods such as focused electron beams, the necessary time for production of such a pattern is a serious limitation for the practical fabrication of nanometer devices. See, for example, U.S. Pat. Nos. 4,103,064 and 4,103,073, Craighead et al, "Ultra-Small Metal Particle Arrays Produced by High Resolution Electron-Beam Lithography", J. Appl. Phys. 53 (11) (Nov. 1982), pp. 7186-7188, Mochel et al "Electron Beam Writing on a 20-.ANG. Scale in Metal .beta.-Aluminas", Appl. Phys. Lett. 42 (4) (Feb. 1983), pp. 392-394, Isaacson "Electrons, Ions and Photons in Submicron Research", Submicron Research, Cornell University (1984), pp. 2814 32.
Attempts have also been made to formulate techniques to fabricate nanometer scale devices "in parallel" wherein a number of devices are made at the same time in a relatively few number of steps. For example, it has been suggested that large biological molecules may be used as a mask to apply a nanometer scale pattern of material on a substrate. Suggestions for the particular large molecule to be employed have included DNA and denatured proteins. See Carter, "Molecular Level Fabrication Techniques and Molecular Electron Devices", J. Vac. Sci. Technol. B1 (4) (Oct.-Dec. 1983), pp. 959-968, Carter, "Biotechnical Synergism in Molecular Electronics", Nonlinear Electrodynamics in Biological Systems, Plenum Press, pp. 260-273 and Tucker, "Biochips: Can Molecules Compute?", High Technology, Vol. 4, No. 2 (Feb. 1984), pp. 36-47 and 79, see particularly p. 46.